1. Field of the Invention
The technical field of the present specification relates to a method for producing a Group III nitride semiconductor light-emitting device which allows stable doping of a p-type semiconductor layer with Mg.
2. Background Art
One type of Group III nitride semiconductor light-emitting device includes an n-type contact layer, an n-type cladding layer, a light-emitting layer, a p-type cladding layer, a p-type contact layer, an n-electrode, and a p-electrode. Preferably, the p-type contact layer and the p-electrode are in good Ohmic contact with each other. When the contact resistance between the p-type contact layer and the p-electrode is high, the driving voltage is high accordingly.
For example, Patent Document 1 discloses a light-emitting diode 10 including a second contact layer 62, and a first contact layer 63 having a higher Mg concentration than the second contact layer 62 (see paragraph [0011] and FIG. 1 in Patent Document 1). Patent Document 1 describes that the Ohmic contact between the p-type contact layer and the p-electrode is thereby improved, and this allows the light-emitting device obtained to have a low driving voltage (see paragraph [0009] in Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. H08-097471
When the electrical resistance of the p-type cladding layer is high, the driving voltage is high accordingly. Therefore, it is preferable to reduce the electrical resistance of the p-type cladding layer. The p-type cladding layer plays a role in confining electrons within the light-emitting layer. To confine electrons, it is preferable that a p-type impurity is present at a high concentration in the p-type cladding layer. Particularly, it is preferable that the concentration of the p-type impurity is high in the vicinity of the boundary between the light-emitting layer and the p-type cladding layer. However, it is by no means easy to increase the concentration of the p-type impurity steeply within the p-type cladding layer. The steepness of the increase in the p-type impurity concentration may vary among production lots. Therefore, the driving voltage of the light-emitting device may vary greatly among production lots.
It is preferable to increase the concentration of Mg steeply also within a p-type semiconductor layer other than the p-type cladding layer. This is because a semiconductor light-emitting device with a low driving voltage can be realized.